3 4 S U P P L E M E N T T O O U T P A T I E N T S U R G E R Y M A G A Z I N E J U LY 2 0 1 7
On a capnography monitor, you see a real-time waveform (capnogram) — a
normal waveform appears as a square-shaped or rectangular box — and a
numeric reading (capnometry) showing the measurement of exhaled CO
2
.
"Normal" end tidal CO
2
is in the range of 35 to 45 mmHg. If the patient's respira-
tory rate increases (hyperventilation), the CO
2
waveform becomes smaller than
the baseline and more frequent, and the numeric reading falls below the normal
range. If respiration decreases (hypoventilation), the waveform becomes taller
and less frequent, and the numeric reading rises above the normal range. If the
square waveform starts to collapse, there's an airway obstruction. If the square
becomes a flat line, the patient is not breathing.
I began my healthcare career when pulse oximetry was considered a wonder-
ful new monitoring tool. It still useful, but it also has its limitations. For exam-
ple, if you see a troublesome oxygen saturation reading, you may simply choose
to increase the oxygen flow without considering the potential causes for the
change, such as a medication that might be relaxing the patient's airway. As a
result, turning up the oxygen would only mask the true nature of the problem.
Also, after a shift in oxygen delivery, several minutes can elapse before a pulse
oximeter provides an accurate reading, meaning the patient may already be in
distress by the time you know it. With capnography, you find out in real time.
Expanded use
Despite its superior ability to detect medication-induced respiratory events,
capnography isn't as ubiquitous as other forms of vital signs monitoring. Why? Cost
may be one barrier to adoption, as capnography can require a significant capital
investment. But I think improving patient outcomes and the potential for saving
lives outweigh budgetary concerns.
In addition, some clinicians may feel confident that monitoring other vital
signs — blood pressure, body temperature, heart rate and blood oxygen levels
— is sufficient. Others may resist adding another monitoring tool to the mix,
because they believe doing so would create additional work without significant
